Progress in plant protoplast research

During the past years plant regeneration from protoplasts was achieved for a number of important crops (maize, sorghum, rice, wheat, sugar beet). The use of embryogenic tissue for protoplast isolation greatly contributed to this success. There was also some progress in woody plant species and ornamentals. Fusion of protoplasts resulted in may fertile hybrid plants, especially in the Brassicaceae and Solanaceae. These somatic hybridization studies led to introduction of new agronomical traits from sexually incompatible species into the cultivar gene pool and to new nucleus‐organelle compositions. The limitations of somatic hybridization, mainly imposed by the taxonomic distance of the parents, and expressed as chromosome loss and reduced fertility, are more clearly recognized now. Asymmetric hybridization with irradiated donor protoplasts resulted in cybrids with new cytoplasmic traits (e. g. intraspecific fusions in Brassica ), as well as in the transfer of only a few donor choromosomes (e. g. intrageneric fusions in Nicotiana ). Most intrageneric fusions, however, resulted only in a limited elimination of donor chromosomes (e. g. in Lycopersicon ), and polyploidization occurred (e. g. in Nicotiana ). Also some success on protoplast transformation was obtained in both monocots and dicots. Fertile transgenic rice plants (Japonica, Indica) were produced after direct gene transfer into protoplasts derived from embryogenic cell suspensions. Particle gun experiments using embryogenic cell suspension of maize resulted in fertile transgenic plants. Transformation of citrus and lettuce by direct gene transfer was also reported.